Unsuccessful attempts to develop a vaccine against HIV have led to a great need for new preventative strategies, the most encouraging of which are microbicides. An effective microbicide would decrease the severity of the AIDS epidemic by decreasing the rate of sexual transmission. A number of models systems have been developed to provide insights into the mechanisms of male-to-female sexual transmission including explant cultures and the rhesus macaque vaginal transmission model. These systems have been successfully used to evaluate and identify candidate microbicides. There has been much less progress in the development of systems to evaluate female-to-male sexual transmission. There are currently no model systems of female-to-male sexual transmission that can determine whether potential microbicides are capable of preventing infection via the penis. To fill this gap, this application seeks to develop an explant culture system using human penile tissue. This will enable the efficacy and safety of candidate microbicides that prevent the sexual transmission of HIV to males to be evaluated. Additionally, my laboratory has recently developed methodology that allows the detection of individual virions in tissue. This system will be further developed to determine how HIV normally interacts with human penile tissue. In the R21 component of this application we will optimize these systems to determine the normal interaction of HIV with intact tissue and subsequent viral replication. In the R33 phase of the application we will evaluate the potential of different candidate microbicides, individually and in combination, to alter HIV interaction with the tissue and prevent HIV infection and replication. We will also determine if exposure to the microbicide causes any changes in the tissue that may have deleterious effects on normal cell function. The application seeks to develop new methods that determine whether chemicals can be used to prevent the sexual transmission of HIV. These methods will be used to determine the potency of protection from HIV infection, and the safety of the compounds before they are tested in humans. It is hoped that preventing HIV infection will decrease the number of people in the world infected with HIV and slow the AIDS epidemic.